SV-POW! … All sauropod vertebrae, except when we're talking about Open Access

The revenge of the controversial hypantra of Argentinosaurus

January 8, 2008

A quick follow-up on Darren’s recent post: the reconstructed Argentinosaurus dorsal in the photo he used seems to be based on the anterior dorsal of the holotype — at the least, the proportions and most of the features are the same — so we can get some more information by looking at the figure of the same element in the description of Bonaparte and Coria (1993). Here it is:

This shows the details better than the photo, though admittedly it’s rather less spectacular. But what’s most noticable, to me at least, is that the centrum and the lower part of the neural arch is completely missing … which means that the “hypantrum” of the reconstructed vertebra in the photo that Darren used is pretty much a complete fiction. Or let’s be more charitable and say “involves a certain amount of interpretation”.

So! What’s the story? The dorsal figured here is the one that Bonaparte and Coria considered to be ?first, but the ?second and ?third (and more posterior dorsals) are also preserved — and more fully, at least in the relevant area. The ?second dorsal, shown in their figure 3, is not illustrated in anterior view, but the ?third is shown in their figure 4:

So now we can see what we came here for: the distinctly ventrolaterally sloping borders of the triangular hollow below the prezygapophyses. But is it a hypantrum? Well, the purpose of a hypantrum is to accept the hyposphene of the vertebra in front: but if this vertebra’s alleged hypantrum were filled by a hyposphene, its neural canal would be almost completely blocked off. So maybe not. And indeed the ?second dorsal of the Argentinosaurus type specimen, figured by B&C93 in posterior view as fig. 3A, doesn’t seem to have anything resembling a hyposphene. So that supports Salgado and Martínez’s (1993) assertion that the “hyposphenes” of Argentinosaurus are in fact just big old centropostzygapophyseal laminae. (Salgado and Bonaparte 2007 cited and reaffirmed this reidentification, but noted that the posterior dorsals of Big-A do seem to have big hyposphenes and hypantra. Unfortunately these don’t seem to be figured in any of the papers we’ve cited here, so who can say?)

At this point, I am going to stop (A) posting all the figures from Bonaparte and Coria 1993, and (B) pontificating … at least until I’ve read Apesteguía (2005) which — for shame — I haven’t, yet. Well, it’s a truly frightening piece of work.

OK, my New Year’s resolution for 2008 is to read the sodding hypantrum paper — the whole thing. Check back on January 1st 2009 to see how I got on.

But really, I think the answer to the question “does Argentinosaurus have hypantra” comes down to the rather boring answer “it depends what you mean by hypantra”. Good figures of the posterior dorsals would help to resolve that (or, better still, a travel grant to go and look at the material).

My New Year’s resolution was to figure out what the heck a read hypantrum looks like. Fortunately, the first google images hit did the trick. Now, if I can just figure out how to work it into ordinary conversation I’ll be the envy of all my friends.

Out of interest I just googled hypantrum. The first hit was for SV-POW! I then tried google images. The third and fourth hits were of pictures that accompanied an article I produced on placodonts (a group of Triassic marine reptiles). My steady encroachment on the whole internet continues…

[…] only a handful of bones. A good example here is the titanosaur Argentinosaurus, which is known from several vertebrae and a few limb bones, but not all from the same individual. It’s a good bet that it massed […]